Levels of omega-6 (n-6) and omega-3 (n-3), long chain polyunsaturated fatty acids (LcPUFAs) such as arachidonic acid (AA; 20:4, n-6), eicosapentaenoic acid (EPA; 20:5, n-3) and docosahexaenoic acid (DHA; 22:6, n-3) impact a wide range of biological activities including immune signaling, inflammation, brain development and function as well as human diseases ranging from cardiovascular disease (including heart disease and stroke), diabetes, cancers, Alzheimer's disease and mental disorders. Two desaturase steps (Δ6 and Δ5) are rate limiting in the conversion of dietary essential, medium chain, 18 carbon PUFAs (McPUFAs) such as LA (18:2, n-6) to AA and α-linolenic acid (ALA, 18:3, n-3) to EPA and DHA (FIG. 1). Marquardt and colleagues first discovered the presence of the fatty acid desaturase (FADS) gene family (the FADS cluster) on chromosome 11q12˜13 in humans that appeared to be essential for the synthesis of LcPUFAs. FADS1 and FADS2 were demonstrated to code for the enzymes, Δ5 and Δ6 desaturase, respectively. Believed to have arisen through gene duplication, FADS1 and FADS2 are both central to LcPUFA biosynthesis. There is considerable linkage disequilibrium (LD) in this region and genome wide association studies (GWAS) and candidate gene studies have consistently identified as many as 100 single nucleotide polymorphisms (SNPs) within FADS1 and FADS2 as determinants of FADS1 and FADS2 desaturase efficiencies and levels of LcPUFAs in circulating, cellular and breast milk lipids.
There are dramatic differences in the genetic capacity of different individuals and populations to synthesize LcPUFAs and these differences are largely due to variation in and around the FADS cluster. When humans consume a modern western diet with very high levels of n-6 medium chain PUFAs and with much lower levels of n-3 medium chain (18 carbon) PUFAs, gene-diet interactions (as a result of variation FADS1 and FADS2) in LcPUFA biosynthesis create LcPUFA deficiencies (specifically n-3 LcPUFAs) in certain individuals within populations and excesses (specifically n-6 LcPUFAs) in others, all leading to human diseases and disorders.
Certain n-6 LcPUFAs, particularly arachidonic acid (ARA), play a key role in orchestrating a wide variety of inflammatory diseases, and consequently, an individual's capacity to synthesize ARA plays a role in the incidence and impact of inflammatory diseases. Numerous gene-wide association and candidate gene studies have now demonstrated that genetic variation in the FADS cluster together with consumption of the modern western diet causes markedly enhanced arachidonic acid levels, biomarkers of human disease, as well as the diseases themselves in certain humans. For example, SNPs in and around the FADS cluster that are associated with excesses of the n-6 LcPUFA, arachidonic acid are also associated with important cardiovascular disease risk factors [total, LDL, and HDL cholesterol, triglycerides, C-reactive protein (CRP) and pro-inflammatory eicosanoids] as well as coronary artery disease, metabolic syndrome and diabetes.
With regard to n-3 LcPUFAs, the n-3 LcPUFA, docosahexaenoic acid (DHA; 22:6, n-3), is the most abundant fatty acid in the brain and retina, constituting 50% of the weight of the neuron's plasma membrane. N-3 LcPUFAs are not only structurally important, as they are essential for proper brain function and development. DHA plays a critical role in neurogenesis; and adequate dietary DHA and other LcPUFAs are essential for visual, neural and cognitive development in the developing fetus and young infants. Dietary LcPUFA intake by pregnant and breast feeding mothers impacts brain development and function of a developing fetus and young child. The second trimester until two years of age appears to be an especially sensitive period of time (FIG. 2). The biosynthetic capacity of mother, developing fetus and young child to make LcPUFAs and particularly DHA has been shown be very important to brain development and function with diet-FADS gene (largely as a result of the modern western diet) interactions leading to cognitive, behavioral deficits and developmental, neurological and mood disorders. Specifically, there have been associations with variation in the FADS cluster and with cognitive development, and in particular, with those mothers and fetuses with little genetic (FADS) capacity to synthesize n-3 LcPUFAs being at highest risk.
Diagnostic surveys in 60,463 adults in 14 countries around the world found mental illness in 26.4% (over 50 million) of people in the US with much lower percentages in developing, especially African countries (e.g., only 4.7% of Nigerians). Additionally, these numbers are increasing dramatically (3 and 35 fold-increase since 1987 in adults and children, respectively, receiving federal aid). Currently, four of the ten leading causes of disability in the US are estimated to be mental disorders. In addition, developmental and neurological disorders (such as attention deficient disorder, autism and obsessive compulsive disorder continue to increase at an alarming rate, particularly in children.
It is not only the fetus and young children who are at risk of omega-3 deficiency; FIG. 3 shows a dramatic decrease in circulating (blood) levels of omega-3 (n-3) LcPUFAs over the past 75 years. Our studies further demonstrate that there are numerous individuals within a given population (African Americans and European Americans) that have very low levels of circulating n-3 LcPUFAs such as DHA (FIG. 4). Numerous studies have examined associations between the fatty acid composition of peripheral blood compartments (red blood cells, plasma or scrum components), and postmortem brain tissue and psychiatric illnesses, mood and developmental disorders and dementia. These studies have found abnormalities in the fatty acid composition when subjects are compared to controls. Major depressive disorder is perhaps the most studied with regard to n-3 LcPUFA composition; a recent meta-analysis of 14 studies concluded that patients with depression had significantly lower n-3 LcPUFAs in blood compartments then control subjects. A few studies have examined postmortem brain tissue. However, McNamara and colleagues found that postmortem orbitofrontal cortex from patients with schizophrenia, bipolar disorder and major depressive disorder all had significantly lower amounts of DHA when compared to control subjects. In regard to developmental disorders such as ADHD, a recent meta-analysis in nine studies (n=586) found significantly lower blood levels of n-3 LcPUFAs in ADHD children versus controls and concluded that n-3 LcPUFAs are reduced in children with ADHD (Hawkey and Nigg. 2014, Clin. Psychological Rev. 34:496-505). The last two decades have shown a dramatic, unexplained rise in the prevalence of autism spectrum disorders (ASD) in children. Although only a few studies have examined associations between LcPUFAs and ASD, these studies suggest higher ratios of n-6 to n-3 LcPUFAs exist due to excess levels in-6 LcPUFAs and deficiencies in n-3 LcPUFAs.
Animal and human studies indicate that the absence of n-3 LcPUFAs during brain formation and later in life can create n-3 LcPUFA deficiencies and have profound adverse consequences for mood and neurological disorders and optimal brain function in adults (Hibbeln et al. 2006. Int Rev Psychiatry 18(2):107-18). Epidemiologically, brain tissue composition and randomized clinical trials have suggested that the western diet has created n-3 LcPUFA deficiencies in significant proportions of humans on western diets (FIGS. 3 and 4) and demonstrated the benefits of dietary n-3 LcPUFAs, especially for uni- and bipolar depression, schizophrenia and attention-deficient/hyperactivity disorder (ADHD). Schizophrenia is particularly interesting where several groups have shown n-3 LcPUFA deficiency is a critical ‘risk factor’. Amminger and colleagues demonstrated that n-3 LcPUFA supplementation dramatically reduced the development of psychosis in individuals at higher risk. Brookes and colleagues showed an association between a SNP in the FADS cluster (FADS1 and FADS2) with ADHD cases. This result is supported by three previous linkage scans for ADHD, two of which have identified a significant linkage peak which is overlapping with the location of the FADS1 and FADS2 genes. It has been shown that ADHD subjects have deficiencies in plasma n-3 LcPUFAs compared to control subjects.
Currently there are no verified available biomarkers for post-traumatic stress disorders (PTSD) to identify who is at risk or who might benefit from a specific therapy. Numerous studies suggest that synatoneogenesis and neuronal plasticity are important for repair of brain tissue injury, including psychological traumas. Levels of n-3 LcPUFAs have been demonstrated to be involved in these processes. A case-control of active-duty suicides indicated lower serum levels of the n-3 LcPUFA, DHA were associated with a marked increase in suicide risk.
Taken together, major differences in the frequencies of FADS variants that vary the synthesis of LcPUFAs in individuals and populations make the possibility of uniform PUFA nutritional recommendations impossible. To understand individual risk of a PUFA-induced inflammatory disorder including cardiovascular disease, diabetes, arthritis, asthma, Alzheimer's disease and cancer caused by making an excess of n-6 LcPUFAs or risk for a PUFA-induced mental, behavioral or neurological disorders including loss of cognitive function caused by an n-3 LcPUFA deficiency, it is beneficial to assess an individual's capacity to make LcPUFAs to assess the risk of aberrant LcPUFA levels either as excesses or deficiencies.
The present invention overcomes previous shortcomings in the art by providing methods and compositions for identifying subjects that have or who are at risk of having omega-3 deficiency (O3D) or omega-6 excess (O6E), as well as methods and compositions for treating such subjects for diseases and disorders associated with O3D or O6E.